Table of Contents

Basic electronic structure calculation

In this exercise, you will perform a first basic electronic structure calculation to obtain the molecular orbitals (MOs) of Ethene: Your calculations will produce a list of occupied and non occupied MOs and a series of *.cube files, that allow the visualization of the orbitals with VMD.

It is recommended to install and run VMD on your local machine. VMD can be downloaded free of charge after registering with your name and email address. To load and render the *.cube files on your local VMD you first have to transfer them from the server to your machine by using one of the transfer tools recommended on the First Login page.

3. Step

Each cube-file contains the electronic density of one MO mapped onto a regular 3D-grid. Not all MOs were written to a cube-file, this is controlled by the PRINT_MO section. Their filenames tell you to which MO a cube-file belongs. For example ethene-WFN_00005_1-1_0.cube contains the 5th orbital.

Use VMD to visualize the cube-files:

Open one .cube file at a time in VMD

To visualize the molecule (sometimes it's not visible by default):
go to Graphics > Representations > Draw style and set Drawing Method to CPK

Add a second representation by clicking on Create Rep

In this second representation set Drawing Method=Isosurfaces and Draw=Wireframe

Finally set the Isovalue of to a reasonable value, eg. 0.1 .

To visualize the positive and the negative part of an orbital simultaneously, you will have to add a third representation with a negative Isovalue, e.g. -0.1 .

To give the two representations different colors, set their Coloring Method=ColorID and choose different ids.

What you get should look similar to this:

Questions

Compare the new input file with the one from the previous exercise: which keywords changed? which section is missing, respectively new? Lookup the description of the changed keywords and sections in the CP2K Manual

From the output: What are the energies of the Highest Occupied MO (HOMO), Lowest Unoccupied MO (LUMO), and the band-gap (in electronvolt)?

Use VMD to identify the shape of the $\pi$ and $\pi^*$ orbitals (submit images like the one from above)

Repeat the calculation for Propene and find again the HOMO, LUMO and band-gap energies.

The eigenvalues are given in Hartree (Eh) while the band-gap is stated directly in electronvolt

Lookup the molecular orbital diagram of Ethen to identify which MOs and therefore which cube files you need to open.